The present invention relates to a photosensitive mixture that can be developed with aqueous solutions, that contains a polymeric binder and a photocurable compound or combination of compounds, and that is suitable for the production of photosensitive recording materials, in particular of planographic printing plates and photoresists.
DE 20 24 244 (=U.S. Pat. No. 3,867,147) relates to photosensitive recording materials comprising co-condensation products of diazonium salts capable of condensation and other, non-photosensitive compounds, capable of condensation, if appropriate combined with polymeric binders, for producing printing plates. These photosensitive materials are distinguished by their high photosensitivity and long print runs. The number of prints obtained is particularly high, if water-insoluble binders, for example, polyvinyl formal, are used, but such layers can only be properly processed by means of developers containing a considerable amount of volatile organic solvents. For ecological reasons it is desirable to develop printing plates with purely aqueous solutions. In the most favorable cases, the printing plates can be developed with relatively aggressive acidic or alkaline purely aqueous solutions by suspending the non-image areas of the layer in the developer, in the form of flakes or relatively small particles. There is, however, the danger of uncontrolled redeposition of flaky matter in non-image areas of the plates whereby the plates are rendered unusable.
EP 152,819 relates to photosensitive mixtures comprising diazonium salt polycondensation products and binders containing carboxyl groups, that are obtained by reacting hydroxyl group-containing polymers with acid anhydrides. Plates produced using these mixtures can be developed with aqueous-alkaline solutions, and the mixtures are suited for the production of lithographic printing forms giving high print runs. It is, however, desirable to achieve even better print runs. For this purpose, the addition of minor amounts of other polymers is proposed, for example, polyurethanes, in order to increase the abrasion resistance. However, this combination results in a poor copying performance, such as undesired dot gain. Furthermore, the developing behavior and shelf life of the plates are impaired. Like other mixtures prepared with carboxyl-containing binders, these mixtures also suffer from the draw-back that upon being processed with developers based on tap water there is the risk of the formation of precipitates in the form of sparingly soluble calcium salts, which are deposited in the developing machines and cause disturbances.
Mixtures of this generic type, where polyurethanes are employed as polymeric binders, are described in U.S. Pat. No. 3,660,097 and DE 27 39 774. It is a disadvantage of these mixtures that the binders are sparingly soluble in the solvents conventionally used for coatings and that the solutions have to be filtered several times to remove insoluble residues. The developability of these mixtures in aqueous-alkaline media is very limited and the print runs are inadequate for high-performance machines.
A similar mixture is described in EP 30,001. The binder contained therein is a branched polyurethane. Using this mixture, relatively high print runs can be achieved, but there are still a number of drawbacks. For example, acidic aqueous developer solutions with an addition of organic solvents are preferably employed for achieving a scum-free, rapid development of the photocured layer. When used for automatic processing, these developers may cause corrosion problems at the light metal parts of the processing equipment.
EP 167 963 describes a negative-working photosensitive mixture which is suitable for the production of planographic printing plates and comprises a diazonium salt polycondensation product, an ethylenically-unsaturated compound which can be polymerized by a free-radical process, a photoinitiator and a water-insoluble polymeric binder. High print runs can be achieved when polyvinyl acetals are used as binders. In this case development can, however, only be performed with solutions that comprise predominantly organic solvents.
EP 274,075 discloses photocurable mixtures which comprise a photocurable substance and a polyvinyl acetal obtained by reacting vinyl alcohol polymers with hydroxy-containing aldehydes. These mixtures, which are suitable for the production of planographic printing plates and photoresists, can be developed with neutral or weakly alkaline aqueous solutions. They give printing plates of relatively high print runs, but the number of prints which can be obtained is inferior to the print run of plates which cannot be developed with purely aqueous solutions.
In DE 37 32 089 graft polymers are described, which comprise a polyurethane as the graft backbone and grafted-on vinyl ester units, which are at least partially saponified to give vinyl alcohol units. The polymers are suitable as binders for pigments; for preparing printing inks, thermoplastic adhesives and solvent-containing adhesives; as constituents of varnishes or coatings for fibers, films and metals, and for thermoplastic shaped articles.
JP 246,047/87 describes photopolymerizable mixtures in which graft polymers of polyurethanes and polyvinyl alcohol with mercapto groups are contained as binders.
Graft polymers obtained from the graft polymers described in DE 37 32 089 above, by acetalizing with aldehydes, are described in German Patent Application P 38 35 840.9.
German Patent Application P 38 24 146.3 discloses photocurable elastomeric mixtures containing a compound polymerizable by a free-radical process, a photoinitiator and, as the binder, a graft polymer according to DE 37 32 089, which is soluble or dispersible in an aqueous solution.